The present invention relates to an intervertebral implant comprising a spacer and a tie for holding the spacer between two vertebrae.
The spacer compensates for a vertebral disk when the disk is deficient and in particular it limits the extent to which the posterior portions of two vertebrae can move towards each other when the spine is extended. The posterior portions of two vertebrae coming too close together gives rise to discomfort, and in particular to pain.
When a vertebral disk has degenerated, movements of the spine can cause contact to be made between vertebrae which can pinch the roots of the nerves that come out laterally between the vertebrae.
To remedy that drawback, it is known to fix at least one spacer between two spinus processes of two consecutive vertebrae. These spinus processes project from the vertebrae in the form of knobbles on the posterior portion of the vertebral column.
Thus, by putting a spacer between two successive spinus processes, the vertebrae are prevented from coming into contact when the vertebral disk is deficient.
However, the spacer must be fixed to the vertebrae in a manner that is sufficiently rigid to keep it in position regardless of the movements of the spine, and it must be sufficiently free relative to the same vertebrae to avoid excessively stiffening the vertebral column. It is known to fix such a spacer, which has one or more through holes formed therein, by means of ligaments inserted in the holes and forming loops into which the spinus processes are engaged. That fixing system is not very rigid and it requires a large number of manipulations, thereby correspondingly increasing the time required for surgery.
An object of the present invention is to provide an intervertebral implant whose means for fixing to the spinus processes are capable of being put into place in a length of time that is relatively short compared with the prior art, and which provides fixing that is more rigid.
To achieve this object, the invention provides an intervertebral implant comprising a spacer in which two opposite notches are formed suitable for receiving the two spinus processes of two vertebrae, each notch defining two flanges each having an inside wall, the implant also having a tie for holding said spacer to said spinus processes, and the implant being characterized in that:
said tie is constituted by at least one strap having a portion surrounding a portion of the surface of the spinus process opposite from the bottom of the notch;
and in that said implant further comprises:
first fixing means formed in at least one flange to fix a first end of said strap; and
self-locking second fixing means formed in at least one other flange, the second end of said strap being inserted through said self-locking fixing means and then pulled to hold said strap in position, thereby securing said spacer to said spinus processes.
It will be understood that the spacer is inserted between two vertebrae and that each of the spinus processes extending therefrom bears against a respective opposite notch in said spacer. The various flexions of the spine give rise to each spinus process having a certain amount of mobility relative to the other, and the spacer is held in position by a strap which provides a contact area with the spinus process that is greater than that provided by a tie of the ligament type.
Consequently, the tie is held more securely to the spinus process. Furthermore, one end of the strap is fixed in one of the two flanges constituting the notch and advantageously the first fixing means comprise a slot formed through said flange, said first end of said strap being suitable for being engaged in said slot in such a manner as to form a loop whereby said first end of said strap is secured to said flange. This method of fixing is relatively easy to install. Thus, the end of the strap is fixed to said spacer by ligating the tip of the strap to a portion of its end after it has passed through said slot and a loop has been formed. This operation is performed prior to installing the spacer between two vertebrae.
The second end of the strap is fixed to said other flange via the self-locking fixing means that preferably comprise a first slot and a second slot that are parallel to each other, said slots being formed through the other flange, said second slot being situated between said first slot and the bottom of the notch such that the portion of the strap which passes through the first slot and projects from said inside wall of said other flange is pressed against the portion of the strap which penetrates into the second slot, thereby enabling the end of said strap to be locked by friction.
Advantageously, said tie has two straps and thus each notch has first fixing means in one of its flanges and self-locking fixing means formed in its other flange so as to enable two straps to be fixed, each strap being suitable for passing round a respective one of the spinus processes, whereby said spinus processes are held independently of each other.
It will be understood that the straps are suitable for being premounted so as to form a loop on each notch. The tip of the second end of each strap is then engaged in each second slot via the inside wall of each of said other flanges and is reinserted into the notch via said first slot so as to project from the inside wall of the flange.
When the spacer is inserted between the vertebrae, the spinus processes pass through the loops and fixing is finished off by pulling on the tips of the straps so as to hold said spinus processes tightly in the notches.
It will also be understood that the self-locking means are used during the tightening operation. The more the strap is tightened on the spinus process, the longer the portion of strap projecting from the inside wall of the flange that is pressed against the portion of the strap which penetrates into the second slot. Thus, the two strap portions are pinched between the inside wall of the flange and the body of the spinus process, thereby preventing said end of the strap from moving relative to the flange.
In a first embodiment, the spacer is fixed in parallel on the spinus processes by means of two separate straps.
In a second embodiment, the spacer is fixed on the spinus processes by means of a single strap.